Technical Field
The present disclosure is directed to a method of forming a sensor having a suspended membrane.
Description of the Related Art
Mobile computing devices such as smart phones and tablets include embedded electronic sensors such as, temperature, humidity, and pressure sensors. These sensors are being included to offer consumers or program developers features that entail sensing, monitoring, or controlling local environmental conditions. Providing additional environmental sensors within smart phones, tablet computers will encourage developers to create applications that provide or utilize the information about the temperature, humidity, and pressure of an environment.
Some existing products contain miniature environmental sensors, such as electronic climate control devices or thermostats. Such sensors can activate furnaces and air conditioners for feedback control of air temperature and humidity. Electronic weather stations also rely on internal temperature sensors, barometric pressure sensors, and humidity sensors. These miniature environmental sensors are fabricated separately, on separate substrates (separate die) from one another, or the sensors are built on one substrate and associated circuitry for signal processing and control is fabricated on a separate die.
These sensors are typically formed using silicon based free standing structures, such as structures formed by forming epitaxial layers of silicon and removing portions of the epitaxial layers for form the structures. Alternatively, several wafers are stacked, such that one is a base or support substrate and another, on top of the base, is etched to form the free standing structures. A membrane is supported by the free standing structures and separated from the base by a distance. Due to process limitations it is difficult to form free standing structures and a membrane that is separated from the base by more than four microns. The processes used to form these free standing structures are not compatible with forming integrated circuits on a same die as the free standing structures. Typically, the free standing structure is formed in one die and the integrated circuits are formed in another. The two die are bonded together such that the features are not on a single die. This leads to larger packages and a larger foot print on the printed circuit board of a device that incorporates such a sensor.